Methods of making substitutionally carbon-doped crystalline Si-containing materials by chemical vapor deposition

ABSTRACT

Methods of making Si-containing films that contain relatively high levels of substitutional dopants involve chemical vapor deposition using trisilane and a dopant precursor. Extremely high levels of substitutional incorporation may be obtained, including crystalline silicon films that contain 2.4 atomic % or greater substitutional carbon. Substitutionally doped Si-containing films may be selectively deposited onto the crystalline surfaces of mixed substrates by introducing an etchant gas during deposition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/649,990, filed Feb. 4, 2005; U.S. Provisional Application No.60/663,434, filed Mar. 18, 2005; and U.S. Provisional Application No.60/668,420, filed Apr. 4, 2005; all of which are hereby incorporated byreference in their entireties.

This application is related to, and incorporates by reference in theirentireties, the following U.S. patent applications: U.S. patentapplication No. 11/343,264, entitled “SELECTIVE DEPOSITION OFSILICON-CONTAINING FILMS and U.S. patent application No. 11/343,244,entitled “METHODS OF MAKING ELECTRICALLY DOPED CRYSTALLINE SI-CONTAININGFILMS, both of which are filed on even date herewith.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates generally to the deposition ofsilicon-containing materials in semiconductor processing. Moreparticularly, this application relates to the deposition ofsubstitutionally-doped silicon-containing films by chemical vapordeposition using trisilane and a dopant source.

2. Description of the Related Art

The electrical properties of semiconductors such as silicon (Si),germanium (Ge) and alloys thereof (SiGe) are influenced by the degree towhich the materials are strained. For example, silicon exhibits enhancedelectron mobility under tensile strain, and silicon-germanium (SiGe)exhibits enhanced hole mobility under compressive strain. Methods ofenhancing the performance of semiconductors are of considerable interestand have potential applications in a variety of semiconductor processingapplications. As is well known, semiconductor processing is mostcommonly employed for the fabrication of integrated circuits, whichentails particularly stringent quality demands, but such processing isalso employed in a variety of other fields. For example, semiconductorprocessing techniques are often employed in the fabrication of flatpanel displays using a wide variety of technologies and in thefabrication of microelectromechanical systems (MEMS).

A number of approaches for inducing strain in Si— and Ge-containingmaterials have focused on exploiting the differences in the latticeconstants between various crystalline materials, e.g., Ge (5.65 Å), Si(5.431 Å) and carbon (3.567 Å for diamond). In one approach, thin layersof a particular crystalline material are deposited onto a differentcrystalline material in such a way that the deposited layer adopts thelattice constant of the underlying single crystal material. For example,strained SiGe layers may be formed by heteroepitaxial deposition ontosingle crystal Si substrates. Because the Ge atoms are slightly largerthan the Si atoms, the deposited heteroepitaxial SiGe follows thesmaller lattice constant of the Si beneath it and thus is compressivelystrained to a degree that varies as a function of the Ge content.Typically, the band gap decreases monotonically from 1.12 eV for pure Sito 0.67 eV for pure Ge as the Ge content in the SiGe increases. Inanother approach, tensile strain is introduced into a thin singlecrystalline silicon layer by heteroepitaxially depositing the siliconlayer onto a strain-relaxed SiGe layer. In this example, theheteroepitaxially deposited silicon is strained because its latticeconstant follows the larger lattice constant of the relaxed SiGe beneathit. The tensile strained heteroepitaxially deposited silicon typicallyexhibits increased electron mobility. In these approaches, the strain isdeveloped at the substrate level before the device (e.g., a transistor)is fabricated.

Strain may be introduced into single crystalline Si-containing materialsby substitutional doping, e.g., where the dopants replace Si in thelattice structure. For example, substitution of germanium atoms for someof the silicon atoms in the lattice structure of single crystallinesilicon produces a compressive strain in the resulting substitutionallydoped single crystalline silicon material because the germanium atomsare larger than the silicon atoms that they replace. A tensile strainmay be introduced into single crystalline silicon by substitutionaldoping with carbon, because carbon atoms are smaller than the siliconatoms that they replace. See, e.g., Judy L. Hoyt, “Substitutional CarbonIncorporation and Electronic Characterization of Si_(1-y)C_(y)/Si andSi_(1-x-y)Ge_(x)C_(y)/Si Heterojunctions,” Chapter 3 in“Silicon-Germanium Carbon Alloy,” Taylor and Francis, N.Y., pp. 59-89,2002, the disclosure of which is incorporated herein by reference.

In situ doping is often preferred over ex situ doping followed byannealing to incorporate the dopant into the lattice structure becausethe annealing may undesirably consume thermal budget. However, inpractice in situ substitutional carbon doping is complicated by thetendency for the dopant to incorporate non-substitutionally duringdeposition, e.g., interstitially in domains or clusters within thesilicon, rather than by substituting for silicon atoms in the latticestructure. See, e.g., the aforementioned article by Hoyt.Non-substitutional doping also complicates substitutional doping usingother material systems, e.g., carbon doping of SiGe, doping of Si andSiGe with electrically active dopants, etc. As illustrated in FIG. 3.10at page 73 of the aforementioned article by Hoyt, prior depositionmethods have been used to make crystalline silicon having an in situdoped substitutional carbon content of up to 2.3 atomic %, whichcorresponds to a lattice spacing of over 5.4 Å and a tensile stress ofless than 1.0 GPa. However, prior deposition methods are not known tohave been successful for depositing single crystal silicon having an insitu doped substitutional carbon content of greater than 2.3 atomic %.

Thus, there is a need for improved methods to accomplish in situsubstitutional doping of Si-containing materials. Desirably, suchimproved methods would be capable of achieving commercially significantlevels of substitutional doping without unduly sacrificing depositionspeed, selectivity, and/or the quality (e.g., crystal quality) of thedeposited materials.

SUMMARY OF THE INVENTION

Deposition methods have now been developed that utilize a silicon sourceand a carbon source to deposit carbon-doped Si-containing films. Suchdeposition methods are capable of producing a variety of Si-containingsingle crystal films that are substitutionally doped with carbon tovarious levels, including levels that are significantly higher thanthose achieved using prior methods. For example, preferred depositionmethods using trisilane as a silicon source can be used to deposit avariety of carbon-doped single crystal Si films having a range ofsubstitutional carbon levels, including levels of greater than 2.3atomic %. Other carbon-doped single crystal films, such as phosphorous-and arsenic-doped Si:C, may also be deposited by the methods describedherein.

An embodiment provides a doped single crystalline silicon filmcomprising substitutional carbon, the single crystalline silicon filmhaving a lattice spacing of 5.38 Å or less.

Another embodiment provides a single crystalline silicon film comprising2.4 atomic % or greater substitutional carbon, as determined by x-raydiffraction and Vegard's Law. In preferred embodiments, the singlecrystalline silicon film comprises less than about 0.25 atomic %non-substitutional carbon, more preferably less than about 0.15 atomic %non-substitutional carbon.

Another embodiment provides a method for depositing a single crystallinesilicon film, comprising:

-   -   providing a substrate disposed within a chamber;    -   introducing trisilane and a carbon source to the chamber under        chemical vapor deposition conditions; and    -   depositing a single crystalline silicon film onto the substrate        at a deposition rate of at least about 5 nanometers (nm) per        minute, the single crystalline silicon film comprising at least        1.0 atomic % substitutional carbon, as determined by x-ray        diffraction and Vegard's Law.

Another embodiment provides an integrated circuit comprising a firstsingle crystalline Si-containing region and a second single crystallineSi-containing region, at least one of the first single crystallineSi-containing region and the second single crystalline Si-containingregion comprising an amount of substitutional carbon effective to exerta tensile stress on a third single crystalline Si-containing regionpositioned between the first single crystalline Si-containing region andthe second single crystalline Si-containing region, the third singlecrystalline Si-containing region exhibiting an increase in carriermobility of at least about 10% as compared to a comparable unstressedregion.

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a plot of substitutional carbon content in a silicon filmas a function of deposition pressure for three different carrier gas(H₂) flow rates. FIG. 1B shows a graph of growth rate as a function ofdeposition pressure for three different carrier gas (H₂) flow rates.

FIG. 2A shows a graph of substitutional carbon content in a silicon filmas a function of trisilane flow rate, at a constant monomethylsilane(MMS) flow rate. FIG. 2B shows the substitutional carbon content in thesilicon films as a function of deposition rate (growth rate), at aconstant monomethylsilane (MMS) flow rate.

FIG. 3A shows a graph of substitutional carbon content in a silicon filmas a function of film growth rate, at constant trisilane to MMS flowrate ratios. FIG. 3B shows a graph of growth rate as a function oftrisilane flow rate.

FIG. 4A shows a graph of substitutional carbon content as a function ofgrowth rate for silicon films substitutionally doped with both carbonand arsenic. The graph also shows the resistivity of those films (unitsof mΩ·cm, also left axis). FIG. 4B is a plot showing the growth rate ofthose films as a function of trisilane flow rate.

FIG. 5 shows a graph of substitutional carbon content in anarsenic-doped Si:C film as a function of MMS flow rate, at a constanttrisilane flow rate (200 mg/min) and at a constant arsine flow rate (100sccm of 1% AsH₃ in H₂).

FIG. 6A shows a graph of arsenic-doped Si film resistivity as a functionof growth rate for a series of films deposited at a constant flow rateratio of trisilane to arsine. FIG. 6B shows a graph of film deposition(growth) rate as a function of trisilane flow rate, at a constant flowrate ratio of trisilane to arsine.

FIG. 7 shows a portion of a Fourier Transform Infrared (FTIR) spectrumfor a silicon film substitutionally doped with carbon in accordance withpreferred embodiments.

FIG. 8 is a schematic cross section of a semiconductor substrate afterfield oxide definition, leaving insulator and semiconductor surfacesexposed.

FIG. 9 shows the structure of FIG. 8 after formation of a transistorgate electrode within an active area window.

FIG. 10 shows the structure of FIG. 9 after recessing source and drainregions on either side of the gate electrode.

FIG. 11 shows the structure of FIG. 10 after selective deposition of asemiconductor film within the recessed regions, in accordance with apreferred embodiment.

FIG. 12 shows the structure of FIG. 11 after optional continuedselective deposition, forming elevated source/drain structures.

FIG. 13 shows the structure of FIG. 9 after exposing the semiconductorwindow and conducting a selective deposition to form elevatedsource/drain structures, in accordance with another preferredembodiment.

FIGS. 14A-C show a series of schematic cross sections of a semiconductorsubstrate and illustrate a method of forming source/drain regions byblanket deposition and etching, in accordance with another preferredembodiment.

FIG. 15 shows two graphs illustrating the thermodynamic equilibria ofvarious reactants as a function of temperature for a system includingvarious chlorinated silicon species, with and without the addition ofhydrogen carrier gas.

FIG. 16 is a schematic view of a reactor set up for a system employingtrisilane, a carbon source, an etchant gas, and a carrier gas forselectively depositing silicon-containing films in accordance with apreferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Deposition methods have now been developed that are useful for making avariety of substitutionally doped single crystalline Si-containingmaterials. For example, it has been found that crystalline Si may be insitu doped to contain relatively high levels of substitutional carbon bycarrying out the deposition at a relatively high rate using trisilane asa silicon source and a carbon-containing gas as a carbon source. Inpreferred embodiments, the resulting carbon-doped Si-containing materialis substitutionally doped to a significant degree. For example, thedegree of substitutional carbon doping may be about 70% or greater,preferably about 80% or greater, more preferably about 90% or greater,expressed as the weight percentage of substitutional carbon dopant basedon total amount of carbon dopant (substitutional and non-substitutional)in the silicon. The deposition of carbon-doped layers in accordance withthis aspect can be conducted with or without an etchant gas, selectivelyor non-selectively, as described in greater detail below.

The term “Si-containing material” and similar terms are used herein torefer to a broad variety of silicon-containing materials includingwithout limitation Si (including crystalline silicon), Si:C (e.g.,carbon-doped crystalline Si), SiGe and SiGeC (e.g., carbon-dopedcrystalline SiGe). As used herein, “carbon-doped Si”, “Si:C”, “SiGe”,“carbon-doped SiGe”, “SiGe:C” and similar terms refer to materials thatcontain the indicated chemical elements in various proportions and,optionally, minor amounts of other elements. For example, “SiGe” is amaterial that comprises silicon, germanium and, optionally, otherelements, e.g., dopants such as carbon and electrically active dopants.Thus, carbon-doped Si may be referred to herein as Si:C or vice versa.Terms such as “Si:C”, “SiGe”, and “SiGe:C” are not stoichiometricchemical formulas per se and thus are not limited to materials thatcontain particular ratios of the indicated elements. The percentage of adopant (such as carbon, germanium or electrically active dopant) in aSi-containing film is expressed herein in atomic percent on a whole filmbasis, unless otherwise stated.

The amount of carbon substitutionally doped into a Si-containingmaterial may be determined by measuring the perpendicular latticespacing of the doped Si-containing material by x-ray diffraction, thenapplying Vegard's law (linear interpolation between single crystal Siand single crystal carbon) in a manner known to those skilled in theart. For example, the amount of carbon substitutionally doped into Simay be determined by measuring the perpendicular lattice spacing of thedoped Si by x-ray diffraction, then applying Vegard's law. Those skilledin the art are aware of Vegard's law and the relationships betweensubstitutional carbon level, lattice spacing and strain. See, e.g., JudyL. Hoyt, “Substitutional Carbon Incorporation and ElectronicCharacterization of Si_(1-y)C_(y)/Si and Si_(1-x-y)Ge_(x)C_(y)/SiHeterojunctions,” Chapter 3 in “Silicon-Germanium Carbon Alloy,” Taylorand Francis, N.Y., pp. 59-89, 2002. As illustrated in FIG. 3.10 at page73 of the aforementioned article by Hoyt, the total carbon content inthe doped silicon may be determined by SIMS, and the non-substitutionalcarbon content may be determined by subtracting the substitutionalcarbon content from the total carbon content. The amount of otherelements substitutionally doped into other Si-containing materials maybe determined in a similar manner.

Various embodiments provide methods for depositing carbon-dopedSi-containing materials (such as carbon-doped single crystalline Si)using a silicon source that comprises trisilane, a carbon source and,optionally, source(s) of other elements such as electrical activedopant(s). Under the CVD conditions taught herein, the delivery oftrisilane and a carbon source to the surface of a substrate preferablyresults in the formation of an epitaxial carbon-doped Si-containing filmon the surface of the substrate. In certain selective depositionembodiments described in greater detail below, an etchant gas such aschlorine gas (Cl₂) is delivered to the substrate in conjunction with thetrisilane and carbon source, and the Si-containing film is depositedselectively over single crystal substrates or single crystal regions ofmixed substrates. Methods employing relatively high deposition rates arepreferred, and in preferred embodiments such methods have been found toresult in the deposition of in situ doped crystalline Si-containingmaterials containing relatively high levels of substitutional carbon.

“Substrate,” as that term is used herein, refers either to the workpieceupon which deposition is desired, or the surface exposed to thedeposition gas(es). For example, the substrate may be a single crystalsilicon wafer, or may be a semiconductor-on-insulator (SOI) substrate,or may be an epitaxial Si, SiGe or III-V material deposited upon suchwafers. Workpieces are not limited to wafers, but also include glass,plastic, or any other substrate employed in semiconductor processing.The term “mixed substrate” is known to those skilled in the art, seeU.S. Pat. No. 6,900,115 (issued May 31, 2005), entitled “Deposition OverMixed Substrates,” which is hereby incorporated herein by reference inits entirety and particularly for the purpose of describing mixedsubstrates. As discussed in U.S. Pat. No. 6,900,115, a mixed substrateis a substrate that has two or more different types of surfaces. Forexample, a mixed substrate may comprise a first surface having a firstsurface morphology and a second surface having a second surfacemorphology. In certain embodiments, carbon-doped Si-containing layersare selectively formed over single crystal semiconductor materials whileminimizing and more preferably avoiding deposition over adjacentdielectrics. Examples of dielectric materials include silicon dioxide(including low dielectric constant forms such as carbon-doped andfluorine-doped oxides of silicon), silicon nitride, metal oxide andmetal silicate. The terms “epitaxial”, “epitaxially” “heteroepitaxial”,“heteroepitaxially” and similar terms are used herein to refer to thedeposition of a crystalline Si-containing material onto a crystallinesubstrate in such a way that the deposited layer adopts or follows thelattice constant of the substrate. Epitaxial deposition may beheteroepitaxial when the composition of the deposited layer is differentfrom that of the substrate.

Even if the materials are made from the same element, the surfaces canbe different if the morphologies (crystallinity) of the surfaces aredifferent. The processes described herein are useful for depositingSi-containing films on a variety of substrates, but are particularlyuseful for mixed substrates having mixed surface morphologies. Such amixed substrate comprises a first surface having a first surfacemorphology and a second surface having a second surface morphology. Inthis context, “surface morphology” refers to the crystalline structureof the substrate surface. Amorphous and crystalline are examples ofdifferent morphologies. Polycrystalline morphology is a crystallinestructure that consists of a disorderly arrangement of orderly crystalsand thus has an intermediate degree of order. The atoms in apolycrystalline material are ordered within each of the crystals, butthe crystals themselves lack long range order with respect to oneanother. Single crystal morphology is a crystalline structure that has ahigh degree of long range order. Epitaxial films are characterized by acrystal structure and orientation that is identical to the substrateupon which they are grown, typically single crystal. The atoms in thesematerials are arranged in a lattice-like structure that persists overrelatively long distances (on an atomic scale). Amorphous morphology isa non-crystalline structure having a low degree of order because theatoms lack a definite periodic arrangement. Other morphologies includemicrocrystalline and mixtures of amorphous and crystalline material. Asused herein, “single-crystal” or “epitaxial” is used to describe apredominantly large crystal structure that may have a tolerable numberof faults therein, as is commonly employed for transistor fabrication.The skilled artisan will appreciate that crystallinity of a layergenerally falls along a continuum from amorphous to polycrystalline tosingle-crystal; the skilled artisan can readily determine when a crystalstructure can be considered single-crystal or epitaxial, despite lowdensity faults. Specific examples of mixed substrates include withoutlimitation single crystal/polycrystalline, single crystal/amorphous,epitaxial/polycrystalline, epitaxial/amorphous, singlecrystaudielectric, epitaxial/dielectric, conductor/dielectric, andsemiconductor/dielectric. The term “mixed substrate” includes substrateshaving more than two different types of surfaces, and thus the skilledartisan will understand that methods described herein for depositingSi-containing films onto mixed substrates having two types of surfacesmay also be applied to mixed substrates having three or more differenttypes of surfaces.

Carbon-Doped Si-Containing Films and Methods

An embodiment provides a method for depositing a single crystallinesilicon film, comprising: providing a substrate disposed within a CVDreactor; introducing trisilane and a carbon source to the reactor underchemical vapor deposition conditions; and depositing a singlecrystalline silicon film onto the substrate. The deposition ispreferably carried out at a deposition rate of at least about 5 nm perminute, more preferably at least about 10 nm per minute, even morepreferably at least about 20 nm per minute. Preferably, the resultingsingle crystalline silicon film comprises at least about 1.0 atomic %substitutional carbon, more preferably about 1.5 atomic % or greatersubstitutional carbon, even more preferably 2.4 atomic % or greatersubstitutional carbon, as determined by x-ray diffraction and Vegard'sLaw.

Deposition may be suitably conducted according to the various CVDmethods known to those skilled in the art, but the greatest benefits areobtained when deposition is conducted according to the CVD methodstaught herein. The disclosed methods may be suitably practiced byemploying CVD, including plasma-enhanced chemical vapor deposition(PECVD) or thermal CVD, utilizing trisilane vapor and a carbon source todeposit a single crystalline Si-containing film onto a substrate withina CVD chamber. In some embodiments, the Si-containing film is acarbon-doped epitaxial Si film. In some embodiments, a gaseouschlorine-containing etchant (such as HCl or, more preferably, chlorine)is introduced to the chamber in conjunction with the trisilane andcarbon source to thereby selectively deposit a single crystallineSi-containing film. In the following description, reference may be madeto the use of trisilane and a carbon source to deposit a Si orSi-containing film. It will be recognized that those descriptions arealso generally applicable to the deposition of other Si-containingfilms, e.g., the deposition of SiGe:C films (e.g., involving the use ofa germanium source), to the deposition of electrically doped Si:C andSiGe:C films (e.g., involving the use of a dopant precursor for anelectrical dopant) and to selective depositions (e.g., involving the useof an etchant source), unless otherwise stated. Thermal CVD ispreferred, as deposition can be achieved effectively without the risk ofdamage to substrates and equipment that attends plasma processing.

Trisilane and the carbon source (and, optionally, an etchant gas and/oran electrical dopant precursor, in certain embodiments) are preferablyintroduced to the chamber in the form of separate gases or byintermixing to form a feed gas. The intermixing to form the feed gas maytake place in the chamber or prior to introduction of the feed gas tothe chamber. The total pressure in the CVD chamber is preferably in therange of about 0.001 Torr to about 1000 Torr, more preferably in therange of about 0.1 Torr to about 350 Torr, most preferably in the rangeof about 0.25 Torr to about 100 Torr. Experiments were conducted withpressures ranging from 0.25 Torr to 100 Torr. In some embodiments, thechemical vapor deposition conditions comprise a chamber pressure of atleast about 20 Torr, preferably a chamber pressure in the range of about20 Torr to about 200 Torr. Chamber pressures of about at least about 500mTorr were suitable in single wafer, single pass, laminar horizontalflow reactor in which the experiments were conducted, as describedbelow. The chamber pressure may be referred to herein as a depositionpressure. The partial pressure of trisilane is preferably in the rangeof about 0.0001% to about 100% of the total pressure, more preferablyabout 0.001% to about 50% of the total pressure. The feed gas can alsoinclude a gas or gases other than trisilane and the carbon source, suchas other silicon sources, etchant sources, dopant precursor(s) and/orinert carrier gases, but preferably trisilane is the sole source ofsilicon. The term “dopant precursor(s)” is used herein to refer in ageneral way to various materials that are precursors to various elements(e.g., carbon, germanium, boron, gallium, indium, arsenic, phosphorous,and/or antimony) that may be incorporated into the resulting depositedfilm in relatively minor amounts. It will be recognized that siliconsources may also be considered dopant precursors for the deposition ofSiGe films that contain relatively minor amounts of silicon. Examples ofsuitable carrier gases for the methods described herein include He, Ar,H₂, and N₂. In certain embodiments, the carrier gas is a non-hydrogencarrier such as He, Ar and/or N₂ as described in greater detail below.Preferably, trisilane is introduced to the chamber by way of a vaporizersuch as a bubbler used with a carrier gas to entrain trisilane vapor,more preferably by way of a delivery system comprising a bubbler and agas concentration sensor that measures the amount of trisilane in thecarrier gas flowing from the bubbler. Such sensors are commerciallyavailable, e.g., Piezocon® gas concentration sensors from LorexIndustries, Poughkeepsie, N.Y., U.S.A.

Examples of suitable carbon sources that may be included in the feed gasinclude without limitation silylalkanes such as monosilylmethane,disilylmethane, trisilylmethane and tetrasilylmethane, and/oralkylsilanes such as monomethyl silane (MMS), and dimethyl silane. Insome embodiments, a carbon source comprises H₃Si—CH₂—SiH₂—CH₃(1,3-disilabutane). The feed gas may also contain other materials knownby those skilled in the art to be useful for doping or alloyingSi-containing films, as desired, such as a supplemental silicon source,germanium source, boron source, gallium source, indium source, arsenicsource, phosphorous source, and/or antimony source. Specific examples ofsuch sources include: silane, disilane and tetrasilane as supplementalsilicon sources; germane, digermane and trigermane as germanium sources;monosilylmethane, disilylmethane, trisilylmethane, tetrasilylmethane,monomethyl silane (MMS), and dimethyl silane as sources of both carbonand silicon; and various dopant precursors as sources of electricaldopants (both n-type and p-type) such as antimony, arsenic, boron,gallium, indium and phosphorous. Chlorosilylmethanes of the generalformula (SiH_(3-z)Cl_(z))_(x)CH_(4-x-y)Cl_(y), where x is an integer inthe range of 1 to 4 and where y and z are each independently zero or aninteger in the range of 1 to 3, with the provisos that x+y≦4 and atleast one of y and z is not zero, have been found to be particularlyuseful as sources of carbon, silicon and chlorine. Alkylhalosilanes ofthe general formula X_(a)SiH_(b)(C_(n)H_(2n+1))_(4-a-b) are alsoparticularly useful as sources of carbon, silicon and chlorine, where Xis a halogen (e.g., F, Cl, Br); n is 1 or 2; a is 1 or 2; b is 0, 1 or2; and the sum of a and b is less than 4. Methyldichlorosilane(Cl₂SiH(CH₃)) is an example of an alkylhalosilane of the formulaX_(a)SiH_(b)(C_(n)H_(2n+1))_(4-a-b).

Incorporation of electrically active dopants into Si-containing films byCVD using trisilane is preferably accomplished by in situ doping usingdopant sources or dopant precursors. Preferred precursors for electricaldopants are dopant hydrides, including p-type dopant precursors such asdiborane, deuterated diborane, and n-type dopant precursors such asphosphine, arsenic vapor, and arsine. Silylphosphines, e.g.,(H₃Si)_(3-x)PR_(x), and silylarsines, e.g., (H₃Si)_(3-x)AsR_(x), wherex=0-2 and R_(x)═H and/or deuterium (D), are alternative precursors forphosphorous and arsenic dopants. SbH₃ and trimethylindium arealternative sources of antimony and indium, respectively. Such dopantprecursors are useful for the preparation of preferred films asdescribed below, preferably boron-, phosphorous-, antimony-, indium-,and arsenic-doped silicon, Si:C, SiGe and SiGeC films and alloys.

A suitable manifold may be used to supply feed gas(es) to the CVDchamber. The CVD chamber is preferably in a single wafer reactor, e.g.,a single wafer, horizontal gas flow CVD chamber as described in theillustrated embodiments. Most preferably, the CVD chamber is in asingle-wafer, single pass, laminar horizontal gas flow reactor,preferably radiantly heated. Suitable reactors of this type arecommercially available, and preferred models include the Epsilon™ seriesof single wafer reactors commercially available from ASM America, Inc.of Phoenix, Ariz.: While the methods described herein can also beemployed in alternative reactors, such as a showerhead arrangement,benefits in increased uniformity and deposition rates have been foundparticularly effective in the horizontal, single-pass laminar gas flowarrangement of the Epsilon™ chambers, employing a rotating substrate,particularly with low process gas residence times. CVD may be conductedby introducing plasma products (in situ or downstream of a remote plasmagenerator) to the chamber, but as noted above, thermal CVD is preferred.

The amount of dopant precursor in the feed gas may be adjusted toprovide the desired level of dopant in the Si-containing film. Preferredconcentrations of dopant precursor in the feed gas are in the range ofabout 1 part per billion (ppb) to about 20% by weight based on the totalweight of reactive gas (excluding inert carrier and diluent gases). Forelectrical dopants, preferred concentrations of dopant precursor (e.g.,pure phosphine or equivalent diluted phosphine, arsine or diborane) inthe feed gas are preferably between about 0.1 standard cubic centimetersper minute (sccm) to about 5 sccm, although higher or lower amounts aresometimes preferred in order to achieve the desired property in theresulting film. In the preferred Epsilon™ series of single waferreactors, dilute mixtures of the dopant precursor in a carrier gas canbe delivered to the reactor via a mass flow controller with set pointsranging from about 10 sccm to about 1000 sccm, depending on desireddopant concentration and dopant gas concentration. Dilution of dopantgases can lead to factors of 10⁻⁷ to 10⁻² to arrive at equivalent puredopant flow rates. Typically commercially available dopant sources aredopant hydrides diluted in H2, e.g., 1% arsine or 1% phosphine in H₂.However, as described below with respect to FIGS. 15-16, in someembodiments dopant precursors are diluted in a non-hydrogen inert gas.The dilute mixture is preferably further diluted by mixing withtrisilane, etchant (for selective deposition embodiments), any suitablecarrier gas, and the desired strain-influencing precursor forsubstitutional doping (e.g., for substitutional carbon doping, a carbonsource such as MMS). Since typical total flow rates for deposition inthe preferred Epsilon™ series reactors often range from about 20standard liters per minute (slm) to about 180 slm, the concentration ofthe dopant precursor used in such a method is generally small relativeto total flow.

The relative amounts of the various feed gas components may be variedover a broad range depending on the composition desired for theresulting Si-containing film and the deposition conditions employed(e.g., temperature, pressure, deposition rate, etc.), and may bedetermined by routine experimentation in view of the guidance providedherein. The feed gas components may be intermixed and then delivered tothe chamber or substrate, or the feed gas may be formed by mixing thecomponents at or near the substrate, e.g., by supplying the feed gascomponents to the CVD chamber separately.

Thermal CVD is preferably conducted at a substrate temperature that iseffective to deposit a crystalline Si-containing film over thesubstrate. Preferably, thermal CVD is conducted at a temperature in therange of about 350° C. to about 900° C., more preferably about 500° C.to about 800° C. In an embodiment, the chemical vapor depositionconditions comprise a temperature that is at about a transitiontemperature between substantially mass-transport controlled depositionconditions and substantially kinetically controlled depositionconditions for trisilane. Such trisilane deposition conditions aredescribed in U.S. Pat. No. 6,821,825, which is hereby incorporated byreference and particularly for the purpose of describing trisilanedeposition conditions. PECVD is preferably conducted at a temperature inthe range of about 300° C. to about 700° C. Those skilled in the art canadjust these temperature ranges to take into account the realities ofactual manufacturing, e.g., preservation of thermal budget, depositionrate, different sizes of chambers, including single wafer and batchreactors, preferred total pressures and partial pressures etc. Ingeneral, higher partial pressures entail lower temperatures for a givendesired result, whether it be deposition rate, layer quality or acombination of the two. The substrate can be heated by a variety ofmethods known in the art, e.g., resistive heating and lamp heating.

Various deposition parameters have been found to affect theincorporation of substitutional carbon into Si-containing films,including: the ratio of trisilane to other silicon sources; the ratio ofcarbon source flow rate to trisilane flow rate; the carrier gas flowrate; the deposition pressure; the deposition temperature; and thedeposition rate. Surprisingly, it has been found that certaincombinations of these parameters are particularly advantageous forachieving relatively high levels of substitutional carbon incorporationinto Si-containing films. In particular, the following combinations arepreferred:

-   -   A relatively high trisilane flow rate (e.g., about 100 mg/min to        about 500 mg/min) in combination with at least one of the        following: a relatively low flow rate for supplemental silicon        sources (e.g., a relatively high ratio of trisilane flow rate to        silane flow rate); a relatively low carrier gas flow rate (e.g.,        a relatively high ratio of trisilane flow rate to hydrogen        carrier gas flow rate); a relatively high deposition rate (e.g.,        preferably at least about 5 nm per minute); a relatively high        deposition pressure (e.g., preferably at least about one Torr,        more preferably at least about 20 Torr); a relatively low        deposition temperature (e.g., preferably in the range of from        about 450° C. to about 650° C.); and a relatively high ratio of        carbon source flow rate to trisilane flow rate (e.g., preferably        a MMS to trisilane flow rate ratio of at least about 0.5        scc/mg).    -   A relatively high deposition pressure (e.g., about 20 Torr to        about 200 Torr) in combination with at least one of the        following: a relatively low carrier gas flow rate (e.g., about 1        slm to about 50 slm); a relatively high trisilane flow rate        (e.g., about 100 mg/min to about 500 mg/min); a relatively high        deposition rate (e.g., greater than about 5 nm/min); and a        relatively low deposition temperature (e.g., preferably in the        range of from about 450° C. to about 650° C.).

FIGS. 1-6 illustrate the effects of various combinations of depositionparameters. The data shown in FIGS. 1-6 was obtained for thermalchemical vapor depositions conducted in an Epsilon™ single wafer reactor(commercially available from ASM America, Inc. of Phoenix, Ariz.) usingtrisilane and monomethylsilane (MMS) as a carbon source to deposit aseries of carbon-doped silicon films onto a single crystal siliconsubstrate.

FIGS. 1A and 1B are plots that illustrate the effects of depositionpressure and hydrogen carrier gas flow rates (10, 20 and 40 slm) onsubstitutional carbon content (FIG. 1A) and growth rate (FIG. 1B) usinga trisilane flow rate of 200 mg/min, a MMS flow rate of 180 sccm, and adeposition temperature of 550° C. FIG. 1A shows that increasingdeposition pressure results in higher levels of substitutional carboncontent at all three of the hydrogen carrier gas flow rates employed inthis set of experiments. FIG. 1A also shows that, at various depositionpressures over the range of about 15 Torr to about 100 Torr, reducinghydrogen carrier gas flow rate also results in higher levels ofsubstitutional carbon content.

FIG. 1A shows that the combination of relatively high depositionpressures and relatively low hydrogen carrier gas flow rates isparticularly effective, producing a number of Si:C films that containgreater than 2.3 atomic % substitutional carbon. As noted above, FIG.3.10 at page 73 of the aforementioned article by Hoyt shows that priordeposition methods have been used to make crystalline silicon having asubstitutional carbon content of up to 2.3 atomic %, which correspondsto a lattice spacing of over 5.4 Å and a tensile stress of less than 1.0GPa. FIG. 1A shows that the methods described herein can be used to makein situ carbon-doped crystalline silicon having a substitutional carboncontent that is greater than 2.4 atomic %, a lattice spacing of 5.38 Åor less, and a tensile stress of about 1.0 GPa or greater. Thus, anembodiment provides a doped single crystalline silicon film comprisingsubstitutional carbon, the single crystalline silicon film having alattice spacing of 5.38 Å or less, more preferably about 5.36 Å or less,even more preferably about 5.34 Å or less. Another embodiment provides asingle crystalline silicon film comprising 2.4 atomic % or greatersubstitutional carbon, preferably 2.7 atomic % or greater substitutionalcarbon, even more preferably 3.0 atomic % or greater substitutionalcarbon, as determined by x-ray diffraction and Vegard's Law. Anotherembodiment provides a carbon-doped single crystalline silicon filmhaving a tensile stress of about 1.0 GPa or greater, preferably about1.5 GPa or greater, more preferably about 1.7 GPa or greater, even morepreferably about 1.85 GPa or greater, most preferably about 2.0 GPa orgreater.

In an embodiment, each of the aforementioned carbon-doped singlecrystalline silicon films further comprises an electrical active dopant,e.g., a dopant selected from the group consisting of phosphorous andarsenic, that is electrically active (substitutionally incorporated) asdeposited. In various embodiments, the films contain an amount of theelectrically active dopant that is effective to reduce resistivity,e.g., to provide a Si:C film having a resistivity of about 1.0 mΩ·cm orless, preferably about 0.7 mΩ·cm or less. In another embodiment, each ofthe aforementioned single crystalline silicon films comprises less thanabout 0.3 atomic % non-substitutional carbon, preferably less than about0.25 atomic % non-substitutional carbon, more preferably less than about0.20 atomic % non-substitutional carbon, even more preferably less thanabout 0:15 atomic % non-substitutional carbon.

FIG. 1B shows that reducing hydrogen carrier gas flow rates results inhigher growth rates. FIG. 1B also shows that increasing depositionpressure from about 15 Torr to about 100 Torr generally results inhigher growth rates at all three of the hydrogen carrier gas flow ratesemployed in this set of experiments. Preferred carrier gas flow ratesare in the range of from about 1 slm to about 50 slm, more preferablyabout 10 slm to about 40 slm.

FIGS. 2A and 2B are plots that illustrate the effects of trisilane flowrate (FIG. 2A) and growth rate (FIG. 2B) on substitutional carboncontent at a constant MMS flow rate of 180 sccm, a depositiontemperature of 550° C., a deposition pressure of 15 Torr, and a hydrogencarrier gas flow rate of 20 slm. FIG. 2A shows that increasing thetrisilane flow rate (at constant MMS flow rate) results in lower levelsof substitutional carbon content. The data shown in FIG. 2B are from thesame set of experiments and show that increasing the growth rate (byincreasing the trisilane flow rate as shown in FIG. 2A) at constant MMSflow rate results in lower levels of substitutional carbon content.

FIG. 3A is a plot that illustrates the effects of growth rate onsubstitutional carbon content at various deposition pressures, forcertain fixed MMS to trisilane flow rate ratios. As in FIG. 2, the dataplotted in FIG. 3A were also obtained at a deposition temperature of550° C. and at a hydrogen carrier gas flow rate of 20 slm. FIG. 3A showsthat, at a given flow rate ratio of MMS to trisilane, increasing thegrowth rate results in higher levels of substitutional carbon content.FIG. 3A also shows that, at a given flow rate ratio of MMS to trisilane,increasing the deposition pressure results in higher levels ofsubstitutional carbon content. The combination of relatively highdeposition pressures and relatively high growth rates is particularlyeffective, producing a number of Si:C films that contain greater than2.3 atomic % substitutional carbon.

FIG. 2B shows that, considered in isolation from other depositionparameters, increasing the growth rate without increased carbon sourceflow appears to result in lower levels of substitutional carbon content,whereas FIG. 3A shows that increasing the growth rate results in higherlevels of substitutional carbon content. However, these results are notin conflict because it will be recognized that the data shown in FIG. 2Bwas obtained by increasing the trisilane flow rate at constant MMS flowrate, and thus at decreasing MMS to trisilane flow rate ratios, whereasthe data shown in FIG. 3A was obtained at various fixed MMS to trisilaneflow rate ratios. Thus, the decreases in substitutional carbon contentillustrated in FIG. 2B result from the relatively smaller amount of MMSin the feed gas as the trisilane flow rate is increased, not from theincreased deposition rate per se. At various constant MMS to trisilaneflow rate ratios, increases in trisilane flow rate resulted in increasedgrowth rates as illustrated in FIG. 3B (data obtained at a depositiontemperature of 550° C. and at a hydrogen carrier gas flow rate of 20slm). These increased growth rates produced the higher levels ofsubstitutional carbon content illustrated in FIG. 3A.

Thus, FIG. 3A illustrates the effect of maintaining a constant trisilaneto carbon source ratio while increasing the growth rate bysimultaneously increasing the flow rates of both gases. FIG. 3Ademonstrates that higher levels of substitutional carbon can be achievedat higher growth rates for a given ratio of trisilane to carbonprecursor. FIG. 3B shows that growth rate is a strong positive functionof trisilane flow rate, and that chamber pressure has a relativelymodest effect on growth rate. Thus, taken together, FIGS. 1-3 illustratevarious conditions under which relatively high deposition rates may beused to achieve high levels of substitutional carbon in singlecrystalline silicon.

Although deposition pressure has a relatively modest effect on growthrate, it has been found to substantially affect the crystal quality ofthe deposited Si:C films. For example, in one set of experiments, aseries of epitaxial Si:C films were deposited using trisilane and MMS ata deposition pressure of 15 Torr and a deposition temperature of 550° C.in an Epsilon™ single wafer reactor. At a MMS flow rate of 70 sccm, ahydrogen carrier gas flow rate of 20 slm, and a deposition time of 15minutes, an epitaxial Si:C film having a substitutional carbon contentof 1.92 atomic % and a thickness of 410 Å was deposited. The epitaxialquality of the film was high and essentially all of the carbon wassubstitutional, as indicated by x-ray diffraction. However, increasingthe film thickness and/or carbon content was found to result in lowerepitaxial quality for the resulting Si:C film. For example, a seconddeposition conducted under essentially the same deposition conditions(except for a deposition time of 20 minutes) resulted in a thicker Si:Cfilm having a slightly higher carbon content (1.96 atomic %), but theepitaxial quality of the second film was lower than the first, withx-ray diffraction indicating lower crystallinity. Thus, under theseconditions (including a deposition pressure of 15 Torr), increasing thethickness and carbon content of a Si:C film resulted in a decrease inepitaxial film quality. However, by using a higher deposition pressure,it was found that film thickness and/or carbon content could beincreased while maintaining high epitaxial film quality. For example, athird Si:C film was deposited under essentially the same conditions asthe first film, except that the deposition pressure was higher (40 Torr)and the MMS flow rate was lower (46 sccm). The resulting film had asubstitutional carbon content of 1.99 atomic % and a thickness of 630 Å.Despite the lower MMS flow rate, the substitutional carbon content ofthe third film was slightly higher than the first film, and the growthrate was higher (increased from about 27 nm/min to about 32 nm/min). Inaddition, despite the increase in both thickness and carbon level, theepitaxial quality of the third film was comparable to the first, asdetermined by x-ray diffraction. As another example, a fourth Si:C filmwas deposited under essentially the same conditions as the first andthird films, except that the deposition pressure was higher (90 Torr)and the MMS flow rate was lower (36 sccm). The resulting film had asubstitutional carbon content of 2.27 atomic % and a thickness of 385 Å.Despite the lower MMS flow rate, the substitutional carbon content ofthe third film was significantly higher than both the first and thirdfilms. In addition, the epitaxial quality of the fourth film wascomparable to both the first and third films, as determined by x-raydiffraction

For trisilane depositions conducted in single wafer reactors such as thepreferred Epsilon™ series reactors, trisilane flow rates are suitably inthe range of about 5 mg/min (milligrams per minute) to about 2,000mg/min, preferably in the range of about 50 mg/min to about 500 mg/min,more preferably about 100 mg/min to about 300 mg/min; carbon source(e.g., MMS) flow rates are preferably in the range of about 80 sccm toabout 1000 sccm; ratios of carbon source flow rates to trisilane flowrates are preferably in the range of from about 0.5 standard cubiccentimeters of carbon source per milligram trisilane (scc/mg) to about8.0 scc/mg, more preferably from about 0.9 to about 3.0 scc/mg; carriergas flow rates are preferably in the range of from about 1 slm to about50 slm, more preferably about 10 slm to about 40 slm; deposition ratesare preferably at least about 5 nm per minute, more preferably at leastabout 10 nm per minute; deposition pressures are preferably in the rangeof from about 1 Torr to about 200 Torr, more preferably about 10 Torr toabout 100 Torr, even more preferably about 20 Torr to about 100 Torr;and deposition temperatures in the range of from about 450° C. to about600° C., more preferably in the range of from about 500° C. to about575° C. Those skilled in the art can adapt these conditions to varioustypes of equipment and deposition configurations, using the guidanceprovided herein and routine experimentation. For example, the skilledartisan can readily adapt these conditions to deposit Ge-doped Si andcarbon-doped SiGe.

As mentioned above, the aforementioned carbon-doped single crystallineSi-containing films may further comprise an electrically active dopant,e.g., a dopant selected from the group consisting of phosphorous andarsenic. In general, the presence of substitutional carbon results inscattering that tends to increase resistivity, as compared to anotherwise similar electrically-doped single crystalline Si-containingfilm that does not contain substitutional carbon. However, whendeposited using trisilane as described herein, it has been found thatsuch electrically-doped single crystalline Si-containing films may stillhave surprisingly low resistivities, despite the presence of the carbon.For example, when doped (preferably substitutionally doped) with anelectrical dopant, the single crystalline Si-containing film comprisingsubstitutional carbon may have a resistivity of about 1.0 mΩ·cm or less,preferably about 0.7 mΩ·cm or less. In experiments, a lattice spacing ofabout 5.323 Å (as measured by X-ray diffraction) has now been achievedfor arsenic-doped Si:C deposited from trisilane, arsine and MMS. Thislattice spacing of 5.323 Å corresponds to a substitutional carbon levelof about 3.25%.

For example, FIG. 4A is a graph showing percent substitutional carbon asa function of growth rate (nm/min) for silicon films substitutionallydoped with both carbon and arsenic. FIG. 4A also shows the resistivityof those films (Res, units of mΩ·cm, also left axis). FIG. 4Ademonstrates that Si-containing films may be deposited that containvarious levels of substitutional carbon (e.g., about 1.7 atomic % toabout 3.25 atomic % in the illustrated embodiments) and that containvarious amounts of an electrically active dopant (arsenic in theillustrated embodiment). The combination of the electrically activedopant and the substitutional carbon produces films having desirably lowresistivity values (e.g., about 0.7 mΩ·cm to about 1.45 mΩ·cm in theillustrated embodiments).

A single crystalline silicon film comprising relatively high levels ofsubstitutional carbon as described herein (e.g., films comprising 2.4%or greater substitutional carbon) may exhibit various levels of tensilestress because the substitutional carbon atoms are smaller than thesilicon atoms that they replace in the crystalline silicon latticestructure. In an embodiment, a single crystalline silicon filmcomprising 2.4% or greater substitutional carbon has a tensile stress ofabout 1.0 GPa or greater, e.g., about 1.5 GPa or greater, preferablyabout 1.7 GPa or greater, more preferably about 1.85 GPa or greater,even more preferably about 2.0 GPa or greater. The stress may bedetermined in any particular direction within the film. For example, foroverlying silicon films comprising substitutional carbon that aredeposited onto underlying crystalline silicon substrates, the overlyingsilicon film may exhibit a perpendicular stress (i.e., stress measuredperpendicular to the film/substrate interface) that is different fromthe parallel stress (i.e., stress measured parallel to the filmsubstrate interface). See, e.g., FIG. 3.1 at page 62 of theaforementioned article by Hoyt.

Stress may be introduced by heteroepitaxial deposition of the Si:C filmonto a suitable substrate. For example, an arsenic-doped Si:C filmhaving a substitutional carbon level of about 3.25 atomic % (latticespacing of 5.323 Å) may be deposited onto a single crystal siliconsubstrate. When constrained to such a template (having a lattice spacingof about 5.43 Å), the tensile stress in such a Si:C film amounts to 2.06GPa. The stress may be varied by appropriate selection of the substrateand the amount of substitutional carbon in the Si:C film. In variousembodiments, the stress produced in a heteroepitaxially deposited Si:Cfilm is preferably between 1 GPa and 3 GPa. When the Si:C is depositedto less than the critical thickness of the material, the deposited layerremains tensile stressed. In an embodiment, an electrically doped Si:Cfilm is configured to exert a strain on an adjacent layer. For example,a compressive strain may be exerted on a silicon film that is depositedonto an electrically doped relaxed Si:C layer. In an embodiment, anelectrically doped Si:C film formed in a recessed source/drain regionexerts a tensile strain on a silicon channel formed between the sourceand drain, as described in greater detail below. Such configurations maybe used in various applications, e.g., to improve electron mobility forNMOS devices.

FIG. 4B shows the growth rate of electrically-doped Si:C films as afunction of trisilane flow rate (mg/min). The plots shown in FIGS. 4Aand 4B demonstrate that high levels of substitutional carbon and lowresistivities may be achieved using trisilane by carrying out thedepositions at a relatively high deposition (growth) rate, e.g., atleast about 5 nm/min. As illustrated in FIG. 4B, the growth rates may becontrolled, e.g., by controlling the trisilane flow rates and depositiontemperatures, to produce single crystalline films that comprise variouslevels of carbon, e.g., 2.5% or greater substitutional carbon,preferably 2.6% or greater substitutional carbon, more preferably 2.7%or greater substitutional carbon. In some embodiments, the singlecrystalline films may comprise even higher levels of carbon, e.g., 2.8%or greater substitutional carbon, preferably 2.9% or greatersubstitutional carbon, more preferably 3.0% or greater substitutionalcarbon, as indicated in FIG. 4A.

FIG. 5 shows a graph of substitutional carbon content in anarsenic-doped Si:C film as a function of MMS flow rate, at a constanttrisilane flow rate (200 mg/min) and at a constant arsine flow rate (100sccm). FIG. 5 shows that higher substitutional carbon levels areobtained at higher MMS flow rates under these conditions. Because thetrisilane flow rate was constant and the carbon source (MMS) flow ratewas varied, FIG. 5 illustrates the effect on substitutional carboncontent of varying the flow rate ratio of carbon source to trisilane. Asthe flow rate ratio of MMS to trisilane increased, the amount ofsubstitutional carbon in the resulting film increased relativelylinearly, in accordance with the results discussed above with respect toFIGS. 1-3. FIG. 5 also illustrates that the general principles taughtherein for the deposition of Si:C films are applicable to the depositionof electrically doped Si:C films (e.g., doped with arsenic asillustrated in FIG. 5), with appropriate adaptations using routineexperimentation in light of the guidance provided herein.

FIG. 6A is a graph of arsenic-doped Si film resistivity as a function ofgrowth rate for a series of films deposited at a constant flow rateratio of trisilane to arsine. FIG. 6B is a plot of film deposition rateas a function of trisilane flow rate. FIG. 6 is similar to FIG. 3 in thesense that the data was obtained at a constant flow rate ratio oftrisilane to substitutional dopant precursor (MMS in FIG. 3, AsH₃ inFIG. 6). FIG. 6 demonstrates that silicon film resistivity values ofabout 1.0 mΩ·cm or less may be achieved using trisilane by conductingthe depositions at a relatively high rate, e.g., at least about 5 nm perminute, more preferably at least about 10 nm per minute. As illustratedin FIG. 6B, the growth rate of doped silicon films is a substantiallylinear function of the flow rate of trisilane. FIGS. 3 and 6 demonstratethat the use of trisilane enables relatively high rate depositions thatin turn enable surprisingly high levels of substitutional doping. Thesimilarities among FIGS. 3 and 6, despite the known differences amongcarbon and arsenic, demonstrate that deposition methods using trisilaneas taught herein are relatively insensitive to the nature of the dopantor dopant precursor. Thus, the relatively high rate deposition methodsusing trisilane that are described herein are applicable to a widevariety of dopants (such as carbon, germanium and electrically activedopants), and to the incorporation of those dopants into a wide varietyof Si-containing materials (such as Si, Si:C, SiGe, SiGeC, etc.).Examples of suitable high deposition rates include deposition rates ofabout 5 nm/min or greater, preferably about 10 nm /min or greater. Evenhigher deposition rates may be used, e.g., about 20 nm/min or greater,preferably about 50 nm/min or greater, even more preferably about 100nm/min or greater. Routine experimentation may be used to select highrate deposition conditions applicable to a particular Si-containingmaterial.

In some embodiments, the thickness of a single crystalline silicon filmcomprising a strain-modifying amount of a substitutional dopant such ascarbon as described herein is preferably less than a critical filmthickness. Those skilled in the art understand that a critical filmthickness is a film thickness at which a strained film relaxes under aparticular set of conditions. As the concentration of substitutionaldopant increases, the critical thickness generally decreases. Filmshaving a thickness less than the critical thickness typically remainstrained under those conditions. For example, a single crystallinesilicon film comprising about 1.8 atomic % substitutional carbon mayhave a critical thickness of about 200 nm at 550° C., whereas anotherwise similar film comprising 3.5 atomic % substitutional carbon mayhave a critical thickness of about 25-30 nm at the same temperature.Films having a thickness that is less than a critical thickness for thatfilm will tend to remain strained unless or until sufficiently perturbed(e.g., exposed to sufficient heat to cause relaxation).

FIG. 7 shows a portion of an FTIR spectrum for a crystalline siliconfilm (200 nm thick) substitutionally doped with 1.8 atomic % carbon. Thestrong absorption at about 605 wavenumbers demonstrates the presence ofsubstitutional carbon in the silicon film. The lack of a broadabsorption band at about 450 to 500 wavenumbers demonstrates that thesilicon film contains little (if any) non-substitutional carbon. Thus,an embodiment provides a single crystalline Si-containing filmcomprising 2.4 atomic % or greater substitutional carbon, preferablyabout 2.7 atomic % or greater substitutional carbon, more preferablyabout 3.0 atomic % substitutional carbon, the film comprising less thanabout 0.3 atomic % non-substitutional carbon, preferably less than about0.25 atomic % non-substitutional carbon, more preferably less than about0.20 atomic % non-substitutional carbon, even more preferably less thanabout 0.15 atomic % non-substitutional carbon.

As is known in the art, the lattice constant for single crystal siliconis about 5.431 Å, whereas single crystal germanium has a latticeconstant of 5.657 due to the larger size of the germanium atoms. Thedeviation from silicon's natural lattice constant resulting fromsubstitutional germanium incorporation introduces strain thatadvantageously improves electrical carrier mobility in semiconductors,improving device efficiency. When the SiGe is deposited to less than thecritical thickness of the material, the deposited layer remainscompressively strained and hole mobility is improved for PMOS devices.In such a case, the deposited SiGe layer can be selectively formed,e.g., over an entire active area and can define the channel, or it canact as a relaxed template for forming a compressively strained layerthereover, which can then itself serve as a channel region.

In the embodiments of FIGS. 8-13 (described below), however, the Si:Clayer is selectively formed in recessed source/drain regions 20, and ispreferably deposited under conditions (thickness, temperature) thatmaintain stress. The smaller lattice constant of the Si:C materialfilling the S/D recesses exerts tensile strain on the channel region 22therebetween. Preferably a dopant hydride is added to the process flow,in addition to trisilane, an etchant and a carbon source. Preferably ann-type dopant, and more preferably phosphine or arsine, is employed. ASi:C film comprising substitutional carbon may also be formed insource/drain regions by a blanket deposition and etching sequence, in amanner similar to that illustrated in FIGS. 14A-14C. The processdescribed below for the selective deposition of Si:C in the recessedsource/drain regions 20 may be adapted by those skilled in the art toselectively deposit a variety of Si-containing materials using routineexperimentation in view of the guidance provided herein.

The processes described herein are useful for depositing Si-containingfilms on a variety of substrates, but are particularly useful fordepositing Si-containing films over mixed substrates having mixedsurface morphologies. As noted above, the term “mixed substrate” isknown to those skilled in the art, see U.S. Pat. No. 6,900,115.

An embodiment provides a method for selectively depositing acarbon-doped single crystalline Si-containing film onto the singlecrystal region(s) of a mixed substrate. In addition to the uniformityand high quality films obtained by use of trisilane, as disclosed, e.g.,in U.S. Pat. No. 6,821,825, it has been found that excellent selectivitycan be obtained by the use of trisilane in combination with an etchant,e.g., a chlorine-containing etchant such as HCl , hexachlorodisilane(Si₂Cl₆) or chlorine gas (C1₂). Experiments have shown that selectivitycan be 100% (i.e., with zero deposition on surrounding insulators suchas silicon oxide and silicon nitride). HCl may be provided as an etchantto selective silicon-based deposition processes, where the etch effectsupon slow-nucleating deposition on amorphous (typically insulating)surfaces is greater than the etch effects on exposed semiconductorsurfaces. Chlorine is preferred as HCl is notoriously difficult topurify and typical commercial sources of HCl introduce excessivemoisture into the deposition process. Such moisture can lower theconductivity of deposited films, and cause unacceptable levels ofdefects in epitaxial deposition. Accordingly, the use of a feed gascomprising trisilane, a carbon source and chlorine advantageouslyachieves high levels of selectivity without added etchants, andparticularly without HCl.

Preferably, the feed gas is introduced to the chamber along with ahydrogen carrier gas, using a relatively high trisilane flow rate and arelatively low hydrogen flow rate, as compared to standard use of silaneas the sole silicon precursor. The flow rate of the carbon source isselected to achieve the desired level of incorporation of substitutionalcarbon, as discussed in detail above for the incorporation ofsubstitutional carbon with respect to FIGS. 1-5. For example, in apreferred embodiment thermal CVD is carried out in an Epsilon E2500™,E3000™ or E3200™ reactor system (available commercially from ASMAmerica, Inc., of Phoenix, Ariz.) using a trisilane flow rate of about 5mg/min to 2,000 mg/min, more preferably between about 10 mg/min and 200mg/min, and a carbon source flow rate of about 4 sccm to about 500 sccm.Ratios of carbon source flow rates to trisilane flow rates arepreferably in the range of from about 0.5 scc/mg to about 8.0 scc/mg,more preferably from about 0.9 scc/mg to about 3.0 scc/mg. The hydrogenflow rate may be about 40 standard liters per minute (slm) or less,preferably about 10 slm or less, more preferably about 5 slm or less,and the deposition temperature may be in the range of about 450° C. toabout 700° C., more preferably about 500° C. to about 650° C. Hydrogengas flow rates are preferably minimized during deposition with trisilaneand chlorine-containing etchants. Etchant flow rates are preferablyabout 20 sccm to about 200 sccm. Experiments were carried out withtrisilane flows of 25-400 mg/min, H₂ carrier flow rates of 0-4 slm, andchlorine flow rates of 25-200 sccm. Dopant precursor (e.g., carbonsource and/or electrical dopant precursor) flow rates are typically inthe range of from about 5 sccm to about 500 sccm, depending on thenature of the dopant source and the relative flow rates of the othercomponents. For example, for phosphorus doping, dopant hydride(precursor) flow rates are preferably from 10-200 sccm of phosphine (1%PH₃ in H₂).

FIG. 8 is a schematic cross-sectional view showing a substrate 10comprising a silicon wafer in the illustrated embodiment. The substrate10 can include an epitaxial layer formed over a wafer or an SOIsubstrate. Field isolation regions 12 have been formed by conventionalshallow trench isolation (STI) techniques, defining active areas 14 inwindows among the STI elements. Alternatively, any suitable method canbe used to define field insulating material, including local oxidationof silicon (LOCOS) and a number of variations on LOCOS or STI. It willbe understood that several active areas are typically definedsimultaneously by STI across the substrate 10, and that the STI oftenforms a web separating transistor active areas 14 from one another. Thesubstrate is preferably background doped at a level suitable for channelformation.

FIG. 9 illustrates the substrate 10 after formation of a gate electrode16 over the active area 14. While illustrated as a traditional siliconelectrode, surrounded by insulating spacers and cap layers, andseparated from the underlying substrate 10 by a gate dielectric layer18, it will be understood that the transistor gate stack can have any ofa variety of configurations. In some process flows, for example, thespacers can be omitted. In the illustrated embodiment, the definition ofthe gate electrode 16 defines source and drain regions 20 on either sideof the transistor gate electrode 16 within the active area 14. The gateelectrode 16 also defines a channel region 22 under the gate electrode16 and between the source and drain regions 20.

FIG. 10 illustrates the result of an etch step that selectively removesexposed silicon. Preferably a reactive ion etch (RIE) is employed toensure vertical sidewall definition and minimal damage to exposed oxideand nitride materials. Preferably the depth of the recesses is less thanthe critical thickness of the layer to be deposited in the recessalthough strain on the channel can also be obtained by depositiongreater than the critical thickness. As the exposed silicon isessentially the source and drain (S/D) regions 20 of the active area 14,the etch is referred to as a source/drain recess. It will be understoodthat, in some arrangements, a first step of clearing the thin dielectricover the source/drain regions may be employed.

FIG. 11 shows the result of refilling the recessed S/D regions 20 with aselective deposition process. In particular, the exposed semiconductorsurfaces are cleaned, such as with an HF vapor or HF last dip, leaving apristine surface for epitaxy thereover. Trisilane and chlorine areintroduced as described above, along with a source of substitutionaldopant. For the illustrated embodiment of FIGS. 8-13, the substitutionaldopant comprises a carbon source in order to produce a substitutionallydoped film that creates strain on the channel region, as described inmore detail below. Preferably dopant hydrides are included in theprocess vapor mixture. A silicon-containing epitaxial layer growsselectively in the S/D regions 20. Advantageously, a selectivelydeposited, heteroepitaxial film 30 (comprising, e.g., substitutionallydoped Si:C) fills the S/D regions 20 and exerts strain on the channelregion 22. In the illustrated embodiment, the heteroepitaxial film 30 isapproximately flush with the surface of the channel region 22. Asillustrated, the selective deposition minimizes or avoids depositionover the amorphous regions, e.g., over the insulators include fieldisolation regions 12 (generally a form of silicon oxide) and the spacerscape on the gate electrode 16 (typically silicon nitride).

FIG. 12 illustrates an optional extension of the selective deposition toform elevated S/D regions 20 with the extended heteroepitaxial film 32.As the portion of the extended film 32 below the surface of the channelregion 22 exerts lateral stress on the channel region 22, the portionabove the surface of the substrate need not include as much or anylattice deviation from the natural silicon lattice constant.Accordingly, the carbon source gas can be tapered or halted for theportion of the selective deposition above the surface of the channelregion 22, and trisilane and chlorine flows continued. Electrical dopantsource gases, particularly dopant hydrides such as arsine or phosphine,are preferably continued.

The elevated S/D structure 32 of FIG. 12 advantageously providesadditional silicon material above the surface of the substrate 10. As isknown in the art, through subsequent processing, insulating layers aredeposited and contacts are made through the insulating film to thesource and drain regions 20. The additional silicon material facilitatesformation of silicide contacts, which reduce contact resistance (formohmic contacts). Accordingly, nickel, cobalt or other metal is depositedinto the contact hole and allowed to consume the excess silicon withoutdisturbing electrical properties of shallow junctions for the underlyingsource/drain regions.

FIG. 13 shows another embodiment, in which the structure of FIG. 9 issubjected to the selective deposition using trisilane, a carbon sourceand chlorine, without the intervening S/D recess step. In this case, theselective deposition serves only to raise the source and drain regions,providing excess carbon-doped silicon 34 to permit consumption bycontact silicidation without destroying shallow junctions. Thedeposition can optionally include electrical dopant precursors todeposit Si:C doped with an electrically active dopant. Such electricaldopants are unnecessary, however, if the entire excess silicon structure34 is to be consumed by contact silicidation.

Advantageously, the selective nature of the trisilane/chlorine processobviates subsequent pattern and etch steps to remove excess depositionfrom over field regions. Even imperfect selectivity can advantageouslypermit use of a timed wet etch to remove unwanted deposition overinsulating surfaces, rather than requiring an expensive mask step.Furthermore, superior film quality is obtained at relatively highdeposition rates, improving throughput. For example, certain processembodiments may be used to selectively deposit boron-doped SiGeC usingtrisilane, methylsilane, B₂H₆, and chlorine to form, e.g., a basestructure of a heterobipolar transistor (HBT).

A Si:C layer may be selectively formed in recessed source/drain regions20 as discussed above. However, the Si:C layer may also be formed by aprocess that involves a blanket deposition of the Si:C layer, followedby etching so that single crystalline Si:C remains in the recessedsource/drain regions 20. An embodiment of such a process is illustratedby the sequence shown in FIGS. 14A-14C. FIG. 14A is identical to thestructure shown in FIG. 10 and may be formed in the same manner. Incontrast to the selective deposition process illustrated in FIG. 11however, FIG. 14B shows the result of a blanket deposition process inwhich a heteroepitaxial Si:C film 30 fills the source/drains regions 20,and in which a polycrystalline Si:C film 30 a is deposited over thefield isolation regions 12 and the gate electrode 16. The methodsdescribed above for depositing a single crystalline silicon film thatcomprises substitutional carbon may be employed to deposit the singlecrystalline Si:C film 30 and the polycrystalline Si:C film 30 a. Thesingle crystalline Si:C film 30 is preferably deposited under conditions(thickness, temperature) that maintain stress. As discussed above, thesmaller lattice constant of the Si:C material filling the source/drainrecesses exerts tensile strain on the channel region 22 therebetween.Preferably a dopant hydride is added to the process flow, in addition tothe trisilane and carbon source. Preferably arsine or phosphine areemployed.

FIG. 14C is similar to FIG. 11 above, except that the depicted structureresults from removing the polycrystalline Si:C film 30 a using etchingconditions that are selective for the removal of polycrystallinematerial against single crystal material. Such etching conditions areknown to those skilled in the art.

The process illustrated in FIGS. 14A-14C may be used in varioussituations in which it is desirable to exert a tensile stress on asingle crystalline Si-containing region (such as the channel region 22),and particularly to increase the carrier mobility in the tensilestressed region (the region to which the tensile stress is applied, suchas the channel region 22). Preferably, the carrier mobility (e.g.,electron mobility) is increased by at least about 10%, more preferablyby at least about 20%, as compared to a comparable region that issubstantially identical to the tensile stressed region except that it isnot tensile stressed.

Thus, an embodiment provides an integrated circuit comprising a firstsingle crystalline Si-containing region and a second single crystallineSi-containing region, at least one (preferably both) of the first singlecrystalline Si-containing region and the second single crystallineSi-containing region comprising an amount of substitutional carboneffective to exert a tensile stress on a third single crystallineSi-containing region positioned between the first single crystallineSi-containing region and the second single crystalline Si-containingregion, the third single crystalline Si-containing region exhibiting anincrease in carrier mobility of at least about 10%, more preferably byat least about 20%, as compared to a comparable unstressed region. Theintegrated circuit may comprise one or more transistors in which thefirst single crystalline Si-containing region comprises a source, thesecond single crystalline Si-containing region comprises a drain, andthe third single crystalline Si-containing region comprises a channel.An example of such a transistor is illustrated in FIG. 14C, in which thefirst and second Si-containing regions comprise the source/drain 30, andthe third single crystalline Si-containing regions comprises the channel22.

Deposition of Si-containing films using trisilane as described hereincan offer significant advantages over the use of conventional siliconsources when conducted as described herein. For example, at a givendeposition temperature, deposition of Si-containing films usingtrisilane preferably proceeds at a rate that is significantly fasterthan when silane is used instead of trisilane. A preferred embodimentprovides a high rate deposition method in which trisilane is deliveredto the substrate surface at a delivery rate of about 50-200 mg/min.Under thermal CVD conditions, preferably at a deposition temperature inthe range of about 500° C. to about 800° C., practice of this embodimentresults in relatively fast deposition of the Si-containing material (ascompared to other silicon sources), often at a rate of about 50 Å perminute or higher, preferably about 100 Å per minute or higher, morepreferably about 200 Å per minute or higher. Depositions using trisilanecan be carried out at even higher deposition rates, e.g., about 400 Åper minute or higher, preferably about 800 Å per minute or higher, evenmore preferably about 1,000 Å per minute or higher. Preferably, a dopanthydride source is also delivered to the surface along with the trisilaneand carbon source to improve surface quality and to provide in situdoping.

Preferred Si-containing films have a thickness that is highly uniformacross the surface of the film. When deposition is conducted usingtrisilane as described herein, the percent thickness non-uniformity forthe resulting Si-containing films is preferably about 2% or less.Depending on the mean thickness of the film, additional values forpercent thickness non-uniformity may be preferred as shown in Table 1below. Each value for % thickness non-uniformity shown in Table 1 is tobe understood as if preceded by the word “about.”

TABLE 1 More Preferred Most Preferred Preferred Range of Range of %Range of % Mean Film % Thickness Non- Thickness Non- Thickness Non-Thickness Uniformity Uniformity Uniformity >150 Å <10 <6 <2 100-150 Å<10 <7 <3 50-99 Å <15 <8 <4 <50 Å <20 <10  <5

In general, measurements of film thickness uniformity for a filmdeposited under a particular set of process conditions can be made bydepositing the film on a uniform or mixed substrate having a diameter inthe range of about 200 mm to about 300 mm. Film thickness uniformity isdetermined by making multiple-point thickness measurements along arandomly selected diameter (with no measurements being taken within a 3mm exclusion zone at the wafer periphery), determining the meanthickness by averaging the various thickness measurements, anddetermining the root mean square (rms) variability. A preferredinstrument for measuring film thickness utilizes an Optiprobe™ fromThermawave, and a preferred measurement method involves using such aninstrument to measure the film thickness at 49 points along a randomlyselected wafer diameter. In practice, thickness variability is typicallyobtained directly from the instrument following such a measurement, andthus need not be calculated manually. To enable comparisons, the resultscan be expressed as percent non-uniformity, calculated by dividing therms thickness variability by the mean thickness and multiplying by 100to express the result as a percentage. When measuring thicknessuniformity of a film having a surface that is not accessible to such ameasurement, e.g., a film onto which one or more additional layers havebeen applied, or a film contained within an integrated circuit, the filmis cross sectioned and examined by electron microscopy. The filmthickness is measured at the thinnest part of the cross sectioned filmand at the thickest part, and the range in thickness measurements (e.g.,±6 Å) between these two points is then divided by the sum of the twomeasurements. This non-uniformity is expressed as a percentage herein.

In addition, the compositional uniformity of preferred crystallineSi-containing films that contain other elements (e.g., doped silicon,Si-containing Si:C and SiGe alloys, and doped Si-containing alloys) madein accordance with the methods described herein is materially improvedas compared to corresponding films made without the use of trisilane.This invention is not bound by any theory of operation, but it isbelieved that the Si-containing films have a degree of compositionaluniformity that is better than corresponding Si-containing filmsdeposited using conventional precursors such as silane, dichlorosilane(DCS) or trichlorosilane (TCS). Furthermore, crystalline (e.g., singlecrystalline or polycrystalline) Si-containing alloys containingrelatively high levels of non-silicon element(s) can be prepared by themethods described herein. For example, crystalline Si:C preferablycontains between about 1 atomic % and about 3.5 atomic % ofsubstitutional carbon.

In accordance with another aspect of the invention, for selectivedeposition embodiments a non-hydrogen carrier gas is preferably employedin combination with a substitutional dopant precursor (e.g., a carbonsource), etchant gas and trisilane gas, as described above. Hydrogen gas(H₂) is the most popular carrier gas employed in vapor deposition forsemiconductor processing, and particularly in epitaxial deposition.There are several reasons for the popularity of H₂. H₂ can be providedwith a high degree of purity. Furthermore, the thermal properties ofhydrogen are such that it does not have as great a thermal effect on thewafer. Additionally, hydrogen has a tendency to act as a reducing agent,such that it combats the formation of native oxide that results fromless than perfect sealing of the reaction chamber.

However, particular advantages have now been found from employing anon-hydrogen carrier gas in the substitutional dopantprecursor/trisilane/chlorine deposition system described herein.Preferably helium (He), argon (Ar), neon (Ne), xenon (Xe) or nitrogengas (N2), or a combination of such inert gases, is employed in place ofhydrogen. In the illustrated embodiment, He is employed, as it hasthermal behavior close to that of H₂ and thus entails less tuning of thereactor for the adjustment from use of H₂ carrier gas.

There are a number of possible reaction mechanisms in thetrisilane/chlorine/hydrogen system described hereinabove, including thefollowing:Si(s)+Cl₂(g)→SiCl₂(g) etching   (1)Si₃H₈(g)→H₃SiSiH: (g)+SiH₄(g) trisilane dissociation  (2)H₃SiSiH: (g)→H₂Si═SiH₂(g)   (3)SiH₂(g)+SiCl₂(s)→2Si(s)+2HCl(g) deposition   (4)Si(s)+2HCl⇄SiCl₂(g)+H₂(g) balance of deposition and etching   (5)2PH₃(g)→2P(s)+3H₂(g) doping   (6)PH₃(g)+6Cl(s)→PCl₃(g)+3HCl(g)+free surface sites   (7)Cl₂(g)+H₂(g)→2HCl(g)   (8)Comparison: SiH₂Cl₂(g)→SiCl₂(g)+H₂(g) DCS decomposition

Equation (1) represents an etching reaction in the system. In additionto providing etching (which is needed for selectivity to be maintained),equation (1) also produces a reactant for equation (5) that will tend toproduce silicon deposition. Equation (5) represents a balance betweenreaction to the right (etching) and reaction to the left (deposition).Preferably conditions are such that etching dominates over insulatingsurfaces while deposition dominates over semiconductor windows. Withoutwanting to be limited by theory, it is desirable to provide a sufficientconcentration of chlorine gas to produce etching for selectivity, whileproducing SiCl₂ that provides for deposition.

However, when free H₂ is present as a carrier gas (i.e., in largequantities), reaction (8) will take place, generating HCl. Increasingthe concentration of HCl in the system drives both deposition/etchequations (4) and (5) in the direction of etching, thus driving downdeposition rates for any given “tuned” process. A tuned processrepresents one in which the reactant concentrations have been tuned toachieve selective deposition.

Equation (7) illustrates yet another desirable reaction that isdepressed by generation of HCl due to the presence of H₂ carrier gas.Equation (7) illustrates gettering of chloride adsorbed on the wafersurface. Dopant hydrides, such as arsine, phosphine and diborane(phosphine shown) tend to react with surface chlorine atoms and formvolatile byproduct(s), such that surface reaction sites are freed fordepositions. As with equations (4) and (5), however, increasing the HClconcentration tends to depress the desirable gettering reaction byshifting the equilibrium for equation (7) to the left.

Accordingly, the use of a non-hydrogen carrier gas (which is generallythe dominant gas in the system) will avoid the consumption of Cl₂ byequation (8), thereby avoiding depressing the deposition reactions (4),(5) and the gettering reaction (7). The plots shown in FIG. 15,reproduced from Violette et al., J. Electrochem. Soc., Vol. 143 (1996),pp. 3290-3296 and O'Neill et al., J. Electrochem. Soc., Vol. 144 (1997),pp. 3309-3315, illustrate how the addition of H₂ carrier gas depressesthe concentration of deposition reactant SiCl₂ in the Si/Cl system oftheir studies. Note that, while the process preferably employs no H₂,the benefits of minimizing H₂ can be obtained without total exclusion.Preferably the main carrier gas, representing the largest source of gasin the system is non-hydrogen.

FIG. 16 illustrates a preferred reactor system 100 employing a carriergas (helium in the illustrated embodiment), a carbon source (MMS in theillustrated embodiment), trisilane and an etching gas (Cl₂ in theillustrated embodiment). As shown, a purifier 102 is positioneddownstream of the carrier gas source 104. Some of the inert gas flow isshunted to a vaporizer in the form of a bubbler 106, from which thecarrier gas carries vaporized trisilane 108. Alternatively, thetrisilane can be simply heated to increase the vapor pressure oftrisilane in the space above the liquid, and the carrier gas picks uptrisilane as it passes through that space. In any case, downstream ofthe liquid reactant source container 106 is an analyzer 110 thatdetermines, by measuring the speed of sound through the vapor, thereactant concentration of the flowing gas. Based upon that measurement,the setpoint for the software-controlled downstream mass flow controller(MFC) 112 is altered by the analyzer 110. Such analyzers arecommercially available.

The flow through this MFC 112 merges with the main carrier gas throughthe main carrier gas MFC 114 and other reactants at the gas panel,upstream of the injection manifold 120 for the deposition chamber 122. Asource of etchant gas 130 is also optionally provided for selectivedeposition processes, preferably Cl₂ gas. In the illustrated embodiment,a carbon source 132 (illustrated as MMS) and a source for dopant hydride134 (phosphine shown) are also provided.

As illustrated, the reactor system 100 also includes a centralcontroller 150, electrically connected to the various controllablecomponents of the system 100. The controller is programmed to providegas flows, temperatures, pressures, etc., to practice the depositionprocesses as described herein upon a substrate housed within thereaction chamber 122. As will be appreciated by the skilled artisan, thecontroller 150 typically includes a memory and a microprocessor, and maybe programmed by software, hardwired or a combination of the two, andthe functionality of the controller may be distributed among processorslocated in different physical locations. Accordingly, the controller 150can also represent a plurality of controllers distributed through thesystem 100.

Accordingly, the combination of carbon source/trisilane results inenhanced deposition rates for silicon-containing materials, particularlyepitaxial layers. In one embodiment, the gas flow rates are selected, incombination with pressure and temperature, to achieve selectivedeposition of Si:C on/in semiconductor windows among insulatingmaterial.

In the illustrated embodiment, with the carbon source 132 in combinationwith trisilane and chlorine, selective deposition of high substitutionalcarbon content Si:C can be achieved, as disclosed hereinabove. Inanother embodiment, the dopant hydride source 134 is preferably alsoprovided to produce in situ doped semiconductor layers with enhancedconductivity. Preferably, for Si:C epitaxy, the dopant hydride is arsineor phosphine, and the layer is n-type doped. More preferably, forselective deposition embodiments, the diluent inert gas for the dopanthydride is also a non-hydrogen inert gas. Thus, phosphine and MMS arepreferably stored at their source containers 132, 134 in, e.g., helium.Typical dopant hydride concentrations are 0.1% to 5% in helium, moretypically 0.5% to 1.0% in helium for arsine and phosphine. Typicalcarbon source concentrations are 5% to 50% in helium, more typically 10%to 30% in helium. For example, experiments are being conducted with 20%MMS in helium.

The foregoing discussion about the benefits of non-hydrogen inertcarrier gases in combination with a carbon source, trisilane andchlorine gas is also applicable to other semiconductor compounds. Forexample, trisilane, germane, chlorine and a non-hydrogen carrier gaswill obtain the same enhanced and selective deposition benefits forSiGe. For example, a p-type doped layer can be obtained with theaddition of 1% diborane in helium.

EXAMPLE 1

An eight-inch unpatterned Si<100> wafer substrate was loaded into anEpsilon E2500™ reactor system. The substrate was then introduced intothe reactor system at 900° C., at a hydrogen flow rate of 20 slm, andthe substrate was allowed to stabilize for 1 minute. The hydrogen flowwas then reduced to 2 slm as the temperature of the substrate wasreduced to 550° C. The substrate was then allowed to stabilize for 10seconds, after which time a flow of 50 mg/min of trisilane and 40 sccmof MMS was introduced for 7.5 minutes. A flow of 100 sccm phosphine (1%in H₂) was simultaneously provided and the deposition was conducted at adeposition pressure of about 64 Torr. A continuous, uniformphosphorous-doped Si:C film having a thickness of about 210 nm (XRD) wasdeposited (deposition rate of about 28 nm/min) over the single crystalsubstrate. The substrate was then removed from the reactor and returnedto the loadlock. The phosphorous-doped Si:C film deposited on thesilicon wafer had excellent epitaxial quality, a resistivity of 0.8mΩ·cm (center) and contained about 3.5 atomic % carbon.

EXAMPLE 2

A phosphorous-doped Si:C film was deposited in the manner described inExample 1 except that a patterned substrate having single crystalregions and insulator (oxide) regions was used. The phosphorous-dopedSi:C film formed over both the single crystal and the insulator regions,and had substantially the same thickness (about 200 nm) over both.

All patents, patent applications and papers mentioned herein are herebyincorporated by reference in their entireties. It will be appreciated bythose skilled in the art that various omissions, additions andmodifications may be made to the processes described above withoutdeparting from the scope of the invention, and all such modificationsand changes are intended to fall within the scope of the invention, asdefined by the appended claims.

1. A method for depositing a single crystalline silicon film,comprising: providing a substrate disposed within a chamber; introducingtrisilane and a carbon source to the chamber under chemical vapordeposition conditions, wherein trisilane is introduced to the chamber ata flow rate between about 5 mg per minute and about 2000 mg per minute;and depositing a single crystalline silicon film onto the substrate at adeposition rate of at least about 5 nm per minute, the singlecrystalline silicon film as-deposited comprising at least about 1.0atomic % substitutional carbon dopant, as determined by x-raydiffraction.
 2. The method of claim 1, wherein the single crystallinesilicon film comprises 1.5 atomic % or greater substitutional carbondopant.
 3. The method of claim 1, wherein the single crystalline siliconfilm comprises 2.4 atomic % or greater substitutional carbon dopant. 4.The method of claim 1, comprising depositing the single crystallinesilicon film onto the substrate at a deposition rate of at least about10 nm per minute.
 5. The method of claim 1, comprising depositing thesingle crystalline silicon film onto the substrate at a deposition rateof at least about 20 nm per minute.
 6. The method of claim 1, whereinthe substrate comprises single crystalline silicon.
 7. The method ofclaim 1, wherein the single crystalline silicon film comprises less thanabout 0.25 atomic % non-substitutional carbon.
 8. The method of claim 1,wherein the single crystalline silicon film comprises less than about0.15 atomic % non-substitutional carbon.
 9. The method of claim 1,further comprising introducing a dopant precursor to the chamber. 10.The method of claim 9, wherein the single crystalline silicon filmcomprises an electrically active dopant.
 11. The method of claim 1,wherein the chemical vapor deposition conditions comprise a temperaturein the range of about 450° C. to about 600° C.
 12. The method of claim1, wherein the chemical vapor deposition conditions comprise atemperature that is at about a transition temperature betweensubstantially mass-transport controlled deposition conditions andsubstantially kinetically controlled deposition conditions.
 13. Themethod of claim 1, wherein the chemical vapor deposition conditionscomprise a chamber pressure of at least about 500 mTorr.
 14. The methodof claim 1, wherein the chemical vapor deposition conditions comprise achamber pressure of at least about 20 Torr.
 15. The method of claim 14,wherein the chemical vapor deposition conditions comprise a chamberpressure in the range of about 20 Torr to about 200 Torr.
 16. The methodof claim 1, wherein the carbon source is selected from the groupconsisting of monosilylmethane, disilylmethane, trisilylmethane,tetrasilylmethane, monomethyl silane, dimethyl silane and 1,3-disilabutane.
 17. The method of claim 16, wherein the carbon sourceis monomethylsilane.
 18. The method of claim 1, wherein the carbonsource comprises a chlorosilylmethane of the formula(SiH_(3-z)Cl_(z))_(x)CH_(4-x-y)Cl_(y), where x is an integer in therange of 1 to 4 and where y and z are each independently zero or aninteger in the range of 1 to 3, with the provisos that x+y≦4 and atleast one of y and z is not zero.
 19. The method of claim 1, wherein thecarbon source comprises an alkylhalosilane of the formulaX_(a)SiH_(b)(C_(n)H_(2n+1))_(4-a-b), where X is a halogen; n is 1 or 2;a is 1 or 2; b is 0,1 or2; and the sum of a and b is less than
 4. 20.The method of claim 1, wherein the single crystalline silicon film thatis deposited onto the substrate forms a source region and a drainregion.
 21. A method for depositing a single crystalline silicon film,comprising: providing a substrate disposed within a chamber; introducingtrisilane and a carbon source to the chamber under chemical vapordeposition conditions, wherein trisilane is introduced to the chamber ata flow rate between about 5 mg per minute and about 2000 mg per minute;and depositing a single crystalline silicon film onto the substrate at adeposition rate of at least about 5 nm per minute, the singlecrystalline silicon film as-deposited comprising at least about 1.0atomic % substitutional carbon dopant, as determined by x-raydiffraction, wherein the single crystalline silicon film forms a sourceregion and a drain region and is tensile strained.
 22. The method ofclaim 21, wherein the substrate comprises a channel region positionedbetween the source region and the drain region.
 23. The method of claim22, wherein the channel region is tensile strained.
 24. The method ofclaim 20, wherein the substrate comprises a gate electrode.
 25. Themethod of claim 24, further comprising depositing a polycrystallinesilicon film over the gate electrode while depositing the singlecrystalline silicon film.
 26. The method of claim 25, further comprisingetching the polycrystalline silicon film from over the gate electrode.27. The method of claim 1, wherein trisilane is introduced to thechamber at a flow rate between about 10 mg per minute and about 200 mgper minute.
 28. The method of claim 1, wherein trisilane is introducedto the chamber at a flow rate between about 100 mg per minute and about500 mg per minute.
 29. The method of claim 1, wherein: trisilane isintroduced to the chamber at a flow rate between about 100 mg per minuteand about 500 mg per minute; and the chemical vapor depositionconditions comprise a chamber pressure of at least about 1 Torr.
 30. Themethod of claim 1, wherein: trisilane is introduced to the chamber at aflow rate between about 100 mg per minute and about 500 mg per minute;and the chemical vapor deposition conditions comprise a temperature inthe range of about 450° C. to about 650° C.
 31. The method of claim 1,wherein: trisilane is introduced to the chamber at a flow rate betweenabout 100 mg per minute and about 500 mg per minute; and the carbonsource is introduced to the chamber at a flow rate such that a ratio ofthe carbon source flow rate to the trisilane flow rate is at least about0.5 scc mg ⁻¹.